Help with a regex

I have a text file that would contain the the following type of information - I need to change the format possibly using regex can anyone help with this.

1968 Jan #slide 1 this is the title 01

1988 jan #slide 1 this is the title 01

1988 Jan #slide 2 this is the title 02

jan 1999 slide 3 this is the title 01

CHANGE TO BE

YYYY MM #slide 003 this would the title 01

Many thanks in advance